Multiple frequency intermittent inductive cab signal and automatic train control system



y 22, 1951 L. H. PETER ETAL 2,554,056

MULTIPLE FREQUENCY INTERMITTENT INDUCTIVE CA 1 SIGNAL AND AUTOMATICTRAIN CONTROL SYSTEM Filed June 20, 1947 &

N INVENTORS Lariz'eflam/Pefep and Patented May 22, 1951 MULTIPLEFREQUENCY INTERMITTENT IN- DUCTIVE CAB SIGNAL AND AUTOMATIC TRAINCQNTROL SYSTEM Leslie Hurst Peter and Douglas Goldie Shipp,

London, England, assigncrs, by mesne assignments, to The Union Switch.and. Signal'Company, Swissvale, Pin, a corporation of PennsylvaniaApplication June 20, 1947, Serial No. 755,854 In Great Britain October23, 1946 19 Claims. 1

This invention relates to intermittent inductive train control systemsof the alternating current type, in which wayside inductors located onthe trackway are arranged to influence receiving apparatus on a vehicleso as to effect the control or operation of mechanism on the vehicle togive signal indications, and if desired, to control the train brakes,the trackway inductors comprising circuits adapted to be tuned todifferentfrequencies for this purpose in accordance with the signalaspect of one or more track signals or a control transmitted from anydesired point or automatically in accordance with trafiic conditions.

In systems of this charact'er previously proposed it has been necessaryto provide a source of energy to energize the trackway inductors inorder that they may at times influence the re.- ceiving apparatus on.the vehicle in the desired manner. This, as is evident, is. adisadvantage, especially where it is desired to employ a plurality offrequencies, in that. it entails the installation of a large amount ofapparatus. In the system of. the present. invention this disadvantageisv overcome. and according to the principal feature of the inventionthe trackway inductors. are arranged toinfluence receiving apparatusonthe vehicle when deenergized or when energized by currents the sourcesof supply for which are carried to the vehicle.

According to a further feature of the invention.

two separate sets of receiving apparatus are pro.- vided on the vehicle,both being adapted to be responsive to the influence of the sametrackway inductor, one set, which is adapted to give proceed signalindications being of the normally inactive or zero current output type,while the other set is adapted to give stop signal indications and is ofthe normally active type, for the purpose of insuring increased safetyin operation.

According to a further feature of the invention the stop signalindication mechanism may be combined with or may control arrangementsfor eiiecting an automatic application. of the brakes of'the vehicle ortrain.

One form of apparatus embodying the invention will now be described andthe novel features thereof will then be pointed out in claims.

Referring to the accompanying drawing, Fig. 1 illustrates one form ofapparatus embodying the invention, and Fig. 2 contains a typical trackplan of a stretch of railway track equipped with block signals andillustrates how the apparatus is coordinated with the block signalingsystem.

Similar reference characters refer to similar parts in both views.

Referring to Fig- 2, in the preferred embodiment of the invention, aninductor I situated as shown within or adjacent the trackway, comprisesa core of magnetizable material provided with a winding 2 adapted to bebridged by oneor more of a plurality of tuned circuits 3, eachcomprising. a series connected reactor and condenser. Each circuit istuned to resonance at a different frequency fl, f2 or f3, as indicatedby the legends adjacent the tuned circuits 3, and the number of suchfrequencies will depend uponv the number of signal aspects which can bedisplayed by the associated wayside signal. For example, if the signalis arranged to display four aspects, green (G) double yellow (Y -Y),yellow (Y) and red (R), as illustrated for the signals which governtrain movements into the successive block sections 4T, 3T, 2T and lT, inthe rear of a train V, three resonant circuits will be employed tuned tofrequencies fl, (G), f2 (Y-Y) and f3 (Y) respectively. Contacts 4operated by the signal, or by apparatus controlling the signal, arearranged to bridge the winding of the trackway inductor l with one orother of these resonant circuits in accordance with the proceed aspectdisplayed by the signal and to open circuit the track inductor windingin the event that the signal displays astop (R) indication.

Mounted on the locomotive or other vehicle are two receivers 5 and 6,arranged as shown in Fig. 1 to pass successively over inductor I.Receiver 5 is adapted to control the signal indication device 1 in. thecab of the vehicle, while receiver 6 is employed to provide an automaticapplication of the brakes if the train should pass a signal whichdisplays a stop indication. The output of receiver 5 is arranged to bezero except when passing over a trackway inductor tuned to a frequencyfl, f2 or I3, While the receiver 6 has a normally active output.Receiver 5 will be termed the cabsignal receiver. and receiver 6 thetrain-stop receiver.

The reason. for providing the two separate receivers, one normallyinactive and the other normally active, is to conform to the well-knownrequirement of railway signaling systems that any failure of theapparatus to function normally must not result in a dangerous condition.The manner in which this is achieved will become apparent as-thedescription proceeds.

The cabsignal receiver 5 is of the normally balanced. magnetic bridgetype provided with one or more primary windings 8 which are suppliedwith currents of frequencies 1, f2 and f3 through the tuned circuits 9,by a suitable source carried on the locomotive and. illustratedtypically as a motor-generator set l0, these frequencies correspondingto the frequencies to which the resonant circuits 3 associated with thetrackway inductors are tuned. A. secondary winding II is arranged 3 attimes to supply energizing current to One or other of three quick actingdirect current relays Fl, F2 and F3 through frequency selective circuitsl2 tuned to frequencies fl, f2 and f3 and rectifiers l3. The receiver 5is of the same general type as that disclosed in the Letters Patents ofthe United States to Paul N. Bossart, No. 1,773,297 issued August 19,1930, and No. 1,843,477, issued February 2, 1932. The windings of thereceiver 5 are mounted on cores of magnetizable material separated bythe air gaps a, b, c and d, the reluctance of which is relatively sohigh in comparison with that of the core material that the distributionof the magnetic flux is determined almost wholly by the air gaps, andthe reluctance of the iron portions may be disregarded. The air gaps areso proportioned that when air gap c is not modified by the proximity ofa wayside inductor I, the ratio of the reluctance of the air gap to thatof the compensating air gap 11 is equal to the ratio of the reluctanceof air gap d to that of air gap b. Winding 8 is constantly energized bycurrents of the three frequencies mentioned, and it will be evident thatthe parts are so proportioned that normally the magnetomotive forces dueto these currents will produce a magnetic flux in the core which willdivide between air gaps a and c in the same ratio as between air gaps band d. In other words, one part of the flux will pass through air gaps aand b and the remainder through air gaps c and d. The magnetomotiveforce due to the primary current of each frequency is thus impressedupon the four air gaps in such a manner that these constitutethe fourarms of a magnetic bridge, and they are so proportioned that the bridgeis normally balanced, consequently the primary fluxes normally do notpass through the portion of the secondary core upon which coil II ismounted and the output of the secondary winding ll is normally zero sothat the three quick acting relays Fl, F2 and F3 are normallydeenergized. When the receiver 5 comes into alignment with an inductor Ituned to frequency fl, for example, winding 8 is inductively coupled towinding 2 and causes current of frequency fl to build up therein to itsresonance value, producing an opposing inagnetomotive force which isimpressed across the arm c of the bridge and maintains the bridgesubstantially in balance with respect to this frequency, consequentlyrelay Fl remains deenergized. The fluxes of frequencies f2 and f3however will pass freely through the core of inductor l and thereluctance of arm 0 of the bridge will be materially decreased, withrespect to these frequencies. The receiver 5 will then become unbalancedat frequencies f2 and f3 and electromotive forces at these frequencieswill be induced in the secondary winding ll. Currents of frequencies f2and f3 will accordingly be supplied through the corresponding frequencyselective circuits IE to energize the two quick acting relays F2 and F3,which, with the third relay Fl deenergized, may be arranged in asuitable manner as hereinafter described to cause a G aspect to beindicated on the cab signal indication device. 7 to indicate to theengineman that he has passed a wayside signal showing a green aspect.Similarly, when the wayside signal displays a YY aspect the trackinductor l is tuned to frequency f2 and the secondary winding ll of thereceiver 5 supplies current of frequency fl and f3 to energize the twoquick acting relays Fl and F3 to cause a YY indication to be displayedby device 1. A Y aspect will, as is evident, be obtained in a similarmanner by the energization of relays Fl and F2 when receiver 5 passesover an inductor l tuned to frequency f3, whereas if the track inductorwinding is open circuited, consequent upon the display of a stop aspectR. by the wayside signal, the cab signal inductor will become unbalancedto all frequencies and each of the quick acting relays Fl, F2 and F3will become energized. The prior operation of the train stop receiver 6,in a manner to be described later, will have momentarily released aquick acting relay FIA under these circumstances to disconnect the cabsignal circuits. In this way, an incorrect cab signal will not bedisplayed should one of the cab signal quick acting relays fail tobecome energized or, having become energized, if it should release toclose its back contacts prior to the other cab signal quick actingrelays releasing to open their front contacts. If desired, the quickacting relays Fl, F2, F3 and FlA may be used to operate a gong or otheraudible signal instead of or in addition to the visualindication of thesignal aspects.

The train-stop receiver 6 is of the normally active type and comprises amagnetizable core on which are wound one or more primary windings l5supplied with currents at frequencies fl, f2 and f3 through resonantcircuits Hi from a suitable source of supply which may be the samesource as that which is used to supply the cab signal inductor. The coreof the receiver 6 is provided with extended pole faces separated by anair gap, like the receiver 5, by means of which the winding I5 isinductively coupled with Winding 2 when the receiver is in alignmentwith a wayside inductor so as to maintain the reluctance of its air gapwith respect to flux of the resonant frequency. A portion of the fluxdue to winding l5 passes through a secondary core located in the airgap, upon which is wound a secondary winding l! which normally suppliescurrent of frequencies fl, f2 and f3 induced therein by flux from theprimary winding l5 through frequency selective circuits l8 and rectifierl9 to energize a quick acting relay F, and in addition supplies currentof frequency fl through the frequency selective circuit 23 and rectifier2l to energize the relay FlA. The frequency selective circuits l8 and 23are so arranged that relay F is energized when and only when sufiicientcurrent of one or another of the frequencies fl, f2 or f3 is suppliedfrom the secondary winding l1, and relay FlA is energized when and onlywhen suflicient current of frequency fl is supplied from winding ll.

The train-stop receiver 6 and track inductor l are so proportioned andarranged that when the one passes over the other the secondary windingi! will continue to supply enough current to winding H to maintain relayF or Fl A energized,

A only when the winding of the track inductor is tuned to a frequency towhich the relay is responsive. When the receiver 6 comes into alignmentwith an inductor l tuned to frequency f2, for example, current of thatfrequency builds up in coil 2 to its resonant value to produce anopposing magnetomotive force which prevents a reduction of the flux ofthe same frequency in the core of winding I! and consequently relay Fwill continue to receive sufficient current to remain energized. Thefluxes of frequencies fl and f3 however will pass freely through thecore of inductor l and consequently the fluxes of these frequencies inthe core of winding ll will be diverted or shunted, the reduction in theflux of frequency fl in the core of winding I! being sufficient to causerelay FlA to release. Relay FIA however will pick up again as soon asthe receiver 6 has passed the inductor l. Similarly, relay F will remainenergized and relay FlA release momentarily when receiver 6 passes awayside inductor tuned to frequency f3, while in passing one tuned tofrequency f l, both relays F and FlA will remain energized. It will thusbe seen that, as relay F is arranged to be energized by currents offrequencies fl, f2 or f3, this relay will remain energized whenever thetrain-stop receiver passes over a track inductor the wayside signalassociated with which is showing one of the proceed aspects. Should,however, the way side signal be displaying a stop aspect the trackinductor winding 2 will be open circuited and secondary winding l! ofthe train-stop inductor will accordingly cease to supply current at anyof the three frequencies and relay F will accordingly becomede-energized and will release momentarily. The release of this relay maybe utilized to cause an application of the brakes by releasing a stickrelay MR controlling a normally energized magnet valve MV, as shown orby any other suitable means.

The circuits controlled by the three quick acting relays which areoperated by the cabsignal receiver are so arranged that any signalindication given is held until the next signal location is passed. Asshown in the drawing, this is achieved by arranging the three quickacting relays concerned to act in combination to control three signalindication stick relays GR, YYR and YR by which the lamps of the cabsignal I are selectively lighted. Each signal indication relay isprovided with a stick circuit which includes an energized contact a ofan additional relay FlA controlled by output from the secondarywindingof the train-stop receiver 6. The energizing circuit-for relay FlA includes a frequency selective circuit 20 which passes current offrequency fl only and a rectifier 2|. The result will be that when thetrain stop receiver passes over a track inductor tuned to any frequencyother than frequency fl, as would be the case if the associated signalwere displaying any aspect other than green, relay FlA will release andbreak the stick circuit for that one of the signal indication relayswhich was energized on passing the previous signal location.

Considering now the mode of operation of the apparatus of our invention,it will be assumed that section IT in Fig. 2 is occupied by a train Vlso that the signals in the rear display the aspects indicated in thedrawing and that a second train V2 equipped with the apparatus of Fig. 1is approaching in section 5T. It will also be assumed that relays F andFlA are energized, and that the engineman has operated a reset key 22 tocomplete a circuit from one terminal B of a suitable source of currentthrough relay MR to the other terminal C of the same source, and thatrelay MR has picked up to complete a stick circuit at its contact aextending to terminal 13 over contact a of relay F. The magnet valve MV,the release of which applies the brakes by suitable well-known means isheld energized over contact 17 of relay MR.

When train V2 passes the inductor at the entrance to section 4T, sincethe adjacent signal is displaying its green aspect, contact 4 is in theposition shown, tuning the inductor l to the frequency fl. As receiver 6passes over inductor l, the currents of frequencies f2 and f3 suppliedto relay F drop momentarily to a low value but 6 relay F and likewiserelay FlA are held energized by current of frequency fl. Immediatelythereafter, receiver 5 passes over inductor l and relays F2 and F3 aremomentarily energized to complete a circuit from terminal B at contact 0of relay MR over contacts a. of relays FIA, Fl, F2 and F3 through relayGR to terminal C, and relay GR picks up to complete a stick circuit atits contact a by which it is held energized while the train is insection AT. The operation of contact b of relay GR extinguishes lamp Rand lights lamp G of the cab signaling device I. The gong It sounds atthis time, due to the momentary closing of contacts d of relays F2 andF3.

It will be evident that if the. train entered section 51 with relay GRalready energized to passing the preceding signal at green, the onlyeffect would be a single stroke of the gong l4.

When receiver ii passes over the inductor at the entrance to section 3T,which is tuned to the frequency f2, the currents of frequencies fl andf3 supplied by coil I! drop momentarily to a low value, releasing relayFlA, which by opening its contact a releases relay GR and by closing itscontact 1) causes gong id to sound. When receiver 5 passes over thisinductor, relays F! and F3 pick up momentarily, completing a; circuit attheir contacts I) to pick up the stick relay YYR, and by closing theircontacts 01 causing gong l4 to sound a second time. Lamp G of the device1 is now extinguished and the lamps Y, Y lighted over the front contactsI) and c of relay YYR, this indication being maintained until the trainarrives at the next inductor location.

When receiver ii passes over the inductor at the entrance to section 2T,which is tuned to the frequency f3, relay WA is released in a similarmanner, releasing relay YYR, and when receiver 5 passes over thisinductor, relays Fl and F2 are momentarily energized to pick up relay YRto maintain onl the lower lamp Y lighted. Gong It is caused to soundtwice at this location, as in the preceding example.

If now the train should pass the deenergized inductor at the entrance tothe occupied section lT, relay F as well as relay FlA would be releasedby the operation of receiver ii, releasing relay YR to extinguish lamp Yand to light lamp R of device l, and relay MR would be released todeenergize magnet MV to apply the train brakes, unless the enginemanoperates the reset device 22. Upon the passage of receiver 5 over theinductor at this location relays Fl, F2 and F3 are energized to soundthe gong l4, but without operating any of the cab signal indicationrelays.

It will be seen that the gong M is sounded once at each green signal andis sounded twice at each restrictive signal location.

It will be appreciated that, although in the foregoing example referencehas been made to wayside signals, the invention may equally well beapplied to an installation wherein actuated wayside signals aredispensed with. In this and in other respects various changes andmodifications of the apparatus may be made within the scope of theappended claims without departing from the spirit and scope of theinvention.

Having thus described our invention, what we claim is:

1. An intermittent inductive train control system comprising a trackwayinductor having a winding on a magnetizable core, wayside means fortuning the circuit of said inductor at times to one or another of aplurality of frequencies,

a; first and a second train carried receiver, each having primary andsecondary windings on magnetizable cores arranged to pass successivelyover said inductor, means supplying alternating currents of saidplurality of frequenices continuously to said primary windings, aplurality of relays controllable through tuned circuits by currentsinduced in said secondary windings by the currents in said primarywindings, the cores carrying said secondary windings being so disposedthat a substantial change in the current of each frequency suppliedthereto occurs when the respective receivers pass over said inductor butonly if the circuit for the inductor winding is open or is tuned to adifferent frequency, the relays connected to the secondary winding ofthe first receiver being norm-ally energized and adapted to beselectively released upon passing said inductor and those controlled bythe second receiver being energizable selectively only when passing saidinductor, a plurality of signal indication relays having pick-up andstick circuits, means comprising a front contact of a relay controlledby the first receiver for opening said stick circuits, means comprisingcontacts of the relays controlled by the second receiver for selectivelyclosing said pick up circuits, and a cab signaling device controlled bysaid stick relays.

2. An intermittent inductive train control system comprising a trackwayinductor having a winding on a magnetizable core, a normally opencircuit for said winding, means for completing said circuit at timesthrough selective circuit elements tuned to one or another of aplurality of frequencies, a first and a second train carried receivereach having primary and secondary windings on magnetizable coresarranged to pass successively over said inductor, means supplyingalternating currents of said plurality of frequencies to said primarywindings, the secondary winding of said first receiver being so disposedthat currents of said plurality of frequencies are normally inducedtherein and the current of each frequency is reduced substantially whenthe receiver is over a trackway inductor unless the inductor winding istuned to the same frequency,

the secondary winding of the second receiver being so disposed thatcurrent of each frequency is effectively induced therein only when suchreceiver is over an inductor the winding of which is not tuned to thecorresponding frequency, a plurality of relays connected to saidsecondary windings through selective circuit elements tuned to saiddifferent frequencies, those controlled by the first receiver beingnormally energized and those controlled by the second receiver beingnormally deenergized, a plurality of signal indication relays havingstick circuits controlled by said normally energized relays and pick upcircuits controlled by said normally deenergized relays, and a cabsignaling device controlled by said signal indication relays.

3. An intermittent inductive train control system comprising a trackwayinductor having a winding on a magnetizable core, a first and a secondtrain carried receiver having primary and secondary windings onmagnetizable cores arranged to pass successively over said inductor,means supplying alternating currents of a plurality of frequenciescontinuously to said primary windings, a plurality of relayscontrollable through tuned circuits to respond selectively to currentsinduced in said secondary windings by the currents in said primarywindings, the secondary winding of the first receiver being on a coremagnetically unbalanced with respect to its primary winding so that therelays controlled thereby are energized at all times except when thereceiver is over said inductor, the secondary winding of the secondreceiver being balanced so that the relays controlled thereby areenergized only when the receiver is over said inductor, condensers fortuning the circuit for said inductor winding at times to any of saidfrequencies to prevent an substantial change in the supply of energy ofthe corresponding frequency only, to the secondary winding of eitherreceiver upon passing over said inductor, wayside means effective underrestrictive trafiic conditions for opening the circuit for said inductorwinding and under different proceed traffic conditions for completingsaid circuit through one or another of said condensers to render saidcircuit responsive to different frequencies, a plurality of stick relayscontrolled by said receiver-controlled relays having stick circuitsarranged to be opened thereby when the first receiver passes over saidinductor and pick-up circuits closed selectively thereby when the secondreceiver passes over said inductor, and a cab signaling devicereflecting said traffic conditions controlled by said stick relays.

i. In combination, a train carried receiver including inductivelycoupled primary and secondary windings, means for energizing saidprimary winding by alternating currents of at least two frequencies, tworelays normally energized by current induced in said secondary winding,the circuit for one relay including tuned circuit elements renderingsuch relay selectively responsive to current of one of said frequenciesonly and that for the other relay including tuned circuit elements whichrender it responsive to currents of each of said frequencies, a trackwayinductor cooperating with said receiver comprising a winding on amagnetizable core, and acting to decrease the current of any frequencysupplied to the secondary winding when the receiver passes over saidinductor unless said inductor winding is included in a closed circuittuned to a corresponding frequency, and wayside means for selectivelytuning the circuit for said inductor Winding to one or another of saidfrequencies or for opening said circuit to effect the release of one orboth of said relays or for maintaining both relays energized when thereceiver passes over the inductor.

5. In combination, a train carried receiver including inductivelycoupled primary and secondary windings, means for energizing saidprimary winding by alternating currents of at least two frequencies, tworelays normally energized by current induced in said secondary winding,the circuit for one relay including tuned circuit elements renderingsuch relay selectively responsive to current of one of said frequenciesonly and that for the other relay including tuned circuit elements whichrender it responsive to currents of each of said frequencies, a trackwayinductor cooperating with said receiver comprising a winding on amagnetizable core, and acting to decrease the current of any frequencysupplied to the secondary winding when the receiver passes over saidinductor unless said inductor winding is included in a closed circuittuned to a corresponding frequency, and wayside means which in onecondition opens the circuit for said inductor winding to effect therelease of both said relays, in a second condition closes the circuitfor said winding through circuit elements tuned to one of saidfrequencies to release one of said relays while maintaining the otherrelay energized, and in a third condition closes said circuit throughcircuit elements tuned to another of said frequencies to maintain bothrelays energized while passing said. inductor.

6. In combination, a train carried receiver including inductivelycoupled primary and secondary windings, means normally supplyingalternating currents of two frequencies to said primary winding, tworelays normally energized by current induced in said secondary winding,the circuits for said relays including tuned circuit elements renderingone relay selectively responsive to current of one of said frequenciesand the other relay responsive to current of either frequency, atrackway inductor having a winding and adapted to cooperate with saidprimary winding to materially reduce the current of either frequency insaid secondary winding unless the inductor winding is tuned to the samefrequency, and wayside means which in one condition opens the circuitfor said inductor winding to effect the release of both of said relays,in another condition completes the circuit for said inductor windingthrough circuit elements tuned to one of said frequencies to prevent therelease of either relay, and in a third condition completes said circuitthrough circuit elements tuned to the other of said frequencies toeffect the release of only one of said relays when the receiver passesover said inductor.

7. In combination, a train carried receiver including inductivelycoupled primary and secondary windings, means normally supplyingcurrents of two frequencies to said primary winding, train controllingapparatus governed by current delivered to said secondary winding andadapted to indicate one condition upon a reduction in said currents oftwo frequencies, to indicate a second condition upon a reduction in thecurrent of one frequency only and to indicate a third condition upon areduction in the current of the other frequency only, in said secondarywinding, a wayside inductor having a winding inductively coupled to saidprimary winding when the receiver is adjacent the inductor, saidinductor winding when deenergized being effective to reduce the currentdelivered by the primary winding to said secondary winding to establishsaid one condition, wayside means acting in one condition to open thecircuit for said inductor winding and in other positions to completesaid circuit through circuit elements tuned to one or the other of saidfrequencies to efiect the energization of said inductor winding bycurrent induced therein by the current of the corresponding frequency insaid primary winding, and means including the current in said inductorwinding for preventing a reduction in the current of the correspondingfrequency only delivered to said secondary winding whereby said secondor third condition of said apparatus is indicated depending upon thecondition of said wayside means.

8. In combination, a train carried receiver inluding a primary windingnormally supplied with alternating currents of a plurality offrequencies and a secondary winding having a magnetic circuit balancedwith respect to said primary winding so that normally substantially nocurrent is induced therein, a trackway inductor adapted to unbalancesaid magnetic circuit to cause currents to be induced in the secondarywinding by the currents in the primary winding when the receiver isadjacent the inductor, a

wayside circuit including a winding on said inductor, means for tuningsaid wayside circuit to cause current of any one of said frequencies tobe induced in said inductor winding by current in said primary winding,means including the current induced in said inductor winding formaintaining the magnetic balance of said receiver to prevent theenergization of that one of said relays which is tuned to thecorresponding frequency, and train governing means controlled jointly bysaid frequency responsive relays.

9. In combination with a stretch of railway track divided into blocksections, a plurality of trackway inductors comprising magnetizablecores with windings thereon, each of which is adjacent the track railsin a different block section, a traincarried receiver comprising aprimary winding normally supplied with alternating cur rents of aplurality of frequencies and mounted on a magnetizable core, a secondarywinding on said receiver mounted on a core which is magneticallybalanced so that substantially no current is induced therein by saidprimary winding except when its core is over the core of a trackwayinductor, a plurality of relays connected to said secondary windingsthrough tuned circuit elements by which each is rendered responsive tocurrent of a different one of said frequencies supplied to saidsecondary winding, and means for tuning said inductor winding to aselected one of said frequencies to induce current therein of acorresponding frequency, and means includ-- ing said induced current formaintaining the balance of said secondary winding with respect to saidselected frequency to cause only the relays tuned to the otherfrequencies of said plurality to operate upon the passage of thereceiver over a trackway inductor.

10. In a train control system, a train carried receiver including aprimary and a secondary winding, a plurality of frequency responsiverelays, each responsive to a different frequency, a tuned circuit foreach relay including said secondary winding over which each such relayis energized only when the secondary winding is supplied withalternating current of a corresponding frequency, a source of current ofeach such frequency connected to said primary winding through a tunedcircuit to supply current of a corresponding frequency thereto, atrackway inductor comprising a magnetizable core coopcrating with saidprimary winding to govern the current supplied to said secondarywinding, and means comprising a winding on said inductor core and acircuit for said winding adapted to be tuned to any one of saidfrequencies for selectively controlling the operation of said relays.

11. In a train control system, a trackway inductor having a winding, afirst and a second train carried receiver arranged to pass successivelyover said inductor each having a primary and a secondary winding, meansfor supplying alternating currents of a plurality of frequencies to saidprimary windings, a plurality of wayside circuits including saidinductor winding, each tuned to a diiferent one of said frequencies andadapted to be inductively'energized by the current of correspondingfrequency in said primary windings as the receivers pass over theinductor, means comprising the current of each frequency in the primarywindings of said receivers for inducing current of the correspondingfrequency in the associated secondary windings subject to control bycurrent of the same frequency induced in said inductor winding, aplurality of signal indication stick relays having pick up and stickcircuits, means selectively controlled in accordance with the frequencyof the current supplied to the secondary windings of said receivers foropening said stick circuits when the first receiver passes over saidinductor, means for closing the pick-up circuit for a selected one ofsaid signal indication relays when the second receiver passes over saidinductor, whereby a selected one of said relays becomes energized tocomplete its stick circuit, and a cab signaling device controlledjointly by said signal indication stick relays.

12. In a train control system, a trackway inductor having a winding, afirst and a second train carried receiver arranged to pass successivelyover said inductor, each having a normally energized primary windingadapted to supply energy to said inductor winding and to also supplyenergy at times to the associated secondary winding subject to controlin accordance with the condition of energization of said inductorwinding, wayside means for controlling the energization of said inductorwinding by said primary windings to establish one condition ofenergization under proceed traffic conditions, another under restrictiveconditions and to prevent the energization of said inductor windingunder stop traffic conditions, a plurality of stick relays having pickup and stick circuits, means controlled by the energy supplied to thesecondary winding of the first receiver for opening the stick circuitsfor said relays upon passing said inductor under restrictive or stopconditions, means controlled by the energy supplied to the secondarywinding of the second receiver for closing the pick-up circuit for oneor another of said stick relays to effect its energization and therebyestablish its stick circuit upon passing said inductor under proceed orrestrictive conditions, respectively, and a cab signaling device forindicating said traffic conditions controlled by said stick relays.

13. In a train control system, a trackway inductor having a winding, atrain carried train stop receiver and a cab signal receiver arranged topass successively over said inductor, a primary Winding and a secondarywinding on each receiver, each primary winding being normally energizedby alternating currents of at least two different frequencies andadapted to energize said inductor winding upon passage of the receiverover an inductor, each primary winding cooperating with such inductorwinding to jointly control the energization of the associated secondarywinding, wayside means for conditioning each inductor winding forenergization by current of one frequency or another in accordance withdifferent proceed trailic conditions and for maintaining such inductorwinding deenergized under stop traffic conditions in said stretch, afirst frequency responsive relay, a circuit including the secondarywinding of said train stop receiver effective to maintain said firstrelay energized at all times except when passing over an inductor whichis not energized by current of the frequency to which said first relayis responsive, a plurality of normally deenergized relays, eachresponsive to a different one of said frequencies, means including thesecondary winding of said cab signal receiver for momentarily energizingeach relay of said plurality upon passing over said inductor when theinductor winding is deenergized and acting when said winding isenergized by current of any one of said frequencies for energizing allof the relays of said plurality except the one tuned to that particularfrequency, a cab signaling device, means for releasing said device uponthe energization of said first relay and means responsive to theenergization of all but one of the relays of said plurality for causingsaid device to indicate different proceed traffic conditions dependingupon which of said relays is not energized.

14. In combination with a stretch of railway track divided into blocks,a normally inert trackway inductor for each block having a winding,means including resonant circuit elements for conditioning each inductorwinding for selective energization by currents of different frequenciesin accordance with proceed or restrictive trafiic conditions and foropening the circuit for such winding under stop conditions, meanscarried by a train traversing said stretch for energizing said inductorwindings comprising a train stop receiver and a cab signal receiverarranged to pass successively over each inductor, each such receiverhaving a primary winding normally energized by current of each of thefrequencies to which such inductors are responsive, a cab signalingdevice and a train stop device on said train, a secondary winding oneach receiver adapted to assume different distinctive conditions ofenergization when such receiver is passing over a trackway inductorcorresponding to the condition of energization of said inductor, meanscontrolled in accordance with the condition of the secondary winding ofsaid train stop receiver for actuating said train stop device and forcausing a stop indication to be displayed by said cab signaling deviceupon passing a deenergized inductor, and means controlled in accordancewith the condition of energization of the secondary winding of said cabsignal receiver for indicating trailic conditions as refiected by thecondition of said inductor winding.

15. In combination with a stretch of railway track divided into blocks,a normally inert trackway inductor for each block having a winding,means including resonant circuit elements for conditioning each inductorwinding for selective energization by currents of diiferent frequenciesin accordance with proceed or restrictive traffic conditions and foropening the circuit for such winding under stop conditions, meanscarried by a train traversing said stretch for energizing said inductorwindings comprising a train stop receiver and a cab signal receiverarranged to pass successively over each inductor, each such receiverhaving a primary winding normally energized by current of each of thefrequencies to which such inductors are responsive, a visual cabsignaling device and an audible warning signal on said train, asecondary winding on each receiver adapted to assume differentdistinctive conditions of energization when such receiver is passingover a trackway inductor corresponding to the condition of energizationof said inductor, means controlled in accordance with the condition ofthe secondary winding of said train stop receiver for causing saidwarning signal to sound and said cab signaling device to display a stopindication when passing a deenergized inductor or when passing aninductor energized to indicate restrictive traflic conditions,

and means controlled in accordance with the condition of the secondarywinding of said cab signal receiver for causing said warning signal tosound upon passing each wayside inductor regardless of its energized ordeenergized condition, and in the event such inductor is energized toindicate proceed or restrictive traffic conditions, said means acting tocause the cab signaling device to change its indication from stop to acorresponding proceed or restrictive indication.

16. In combination with a stretch of railway track divided into blocks,a train control system for governing traffic movements over said stretchcomprising a normally inert trackway inductor for each block, means on atrain traversing said stretch for supplying energy successively to saidinductors, comprising a receiver having a primary winding supplied withalternating current of a plurality of frequencies, a winding on eachtrackway inductor arranged to receive energy from said primary windingwhen the train passes over such inductor, wayside circuit controllingmeans for each inductor for conditioning its winding for selectiveenergization under different proceed or restrictive trafilc conditionsby currents of correspondingly different frequencies induced therein byenergy received from said primary winding, and for maintaining theinductor winding deenergized under stop condh tions, means comprising asecondary winding on said receiver effective when passing a trackwayinductor for detecting the condition of the inductor Winding, aplurality of normally deenergized relays, a circuit for each relayincluding frequency responsive elements so arranged that each relay isresponsive to a different one of the frequencies supplied to saidprimary winding, means including said secondary winding for momentarilyenergizing each of said relays upon passing over an inductor the windingof which is deenergized, said means being effective when such inductorwinding is energized by current of any one of said frequencies toenergize all of said relays except the one tuned to the same frequency,a cab signaling device adapted to display different signal aspects, anda plurality of circuits for controlling the aspect displayed by saiddevice, each such circuit including a back contact of a different one ofsaid relays and a front contact of each of the other relays in seriestherewith.

17. In combination with a stretch of railway track divided into blocks,control means for indicating traffic conditions in said blocks, a singlenormally inert trackway inductor for each block, a winding on eachinductor, means including resonant circuit elements selected by saidcontrol means for conditioning each inductor winding for selectiveenergization by currents of different frequencies in accordance withproceed or restrictive traffic conditions and for opening the circuitfor such winding under stop conditions, means carried by a traintraversing said stretch for supplying energy of each of said frequenciesto said inductors as they are passed over by said train, receiving meanson said train comprising two receiver windings arranged to cooperatesuccessively with the winding of each inductor, a cab signaling devic onsaid train, means controlled by the first receiver winding for causing astop indication to be displayed by said device on passing a deenergizedinductor, and means controlled jointly by the first and second receiverwindings for causing proceed or restrictive indications to be displayedby said device in accordance with the frequency of energization of anenergized inductor passed by said train.

18. In combination, a transformer having primary and secondary windingson magnetic cores separated by air gaps, energy sources for constantlysupp ying alternating currents of a plurality of selected frequencies tosaid primary winding, a plurality of relays, a circuit for each relayincluding said secondary winding and resonant circuit elements forselectively energizing different relays by currents of the differentfrequenci s supplied by said secondary winding, a magnetic shunteffective when bridged across at least one of said air gaps to vary theenergy supplied to said relays by said secondary winding by an amountsufficient to effect their control, a winding on said magnetic shuntwhich renders it ineffective at a particular frequency only when saidwinding is included in a closed circuit tuned to the correspondingfrequency, and means for closing the circuit for said winding and tuningit at times to one of said frequencies and at other times to another ofsaid frequencies to effect the selective control of said relays.

19. In combination, a transformer having primary and secondary windingson magnetic cores separated by four air gaps which form the arms of amagnetic bridge, two of said arms being between one end of the primarycore and the opposite ends of the secondary core, the other two armsbeing between said opposite ends of the secondary core and the other endof the primary core, energy sources for constantly supplying alternatingcurrents of a plurality of selected frequencies to said secondarywinding, a plurality of relays, a circuit for each relay including saidsecondary winding and resonant circuit elements for selectivelyenergizing different relays by currents of the different frequenciessupplied by said secondary winding, a magnetic shunt effective whenbridged across one of said air gaps to cause a substantial change in theenergy of each of said frequencies supplied by the secondary winding tosaid relays due to the resulting change in the ratio of said bridgearms, a winding on said magnetic shunt which renders it ineffective at aparticular frequency only when said winding is included in a closedcircuit tuned to the corresponding frequency, and means for closing thecircuit for said winding and tuning it at different times to each ofsaid frequencies to effect the selective control of said relays.

LESLIE HURST PETER. DOUGLAS GOLDIE SHIPP.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Germany "55pm 22, 1921

